1. Field of the Invention
The present invention relates generally to a process for forming metallurgy patterns on a substrate. More particularly, the present invention relates to a process for forming a metallurgy interconnection system with a planar top surface.
2. Description of the Prior Art
Multilevel metallurgy interconnection systems for integrated circuit devices have conventionally been formed by blanket depositing a metal layer, forming a photoresist layer on the metal layer, exposing the photoresist to the desired metallurgy pattern, developing the photoresist and subsequently etching the exposed portions of the metal layer to form the first level of a desired metallurgy interconnection system. The metallurgy pattern was then covered by an insulating layer and another metallurgy pattern was formed on the surface of the insulating layer making contact to the underlying metallurgy pattern through via holes. Each time a metallurgy pattern is deposited on a surface, the more irregular or non-planar the surface of the overlying insulating layer becomes. In general, three levels of metallurgy are the maximum that can be deposited using the above described method.
An alternative method for forming metallurgy patterns is commonly denoted by the term "lift-off method". The lift-off method was initially described in U.S. Pat. No. 2,559,389. Improvements to the basic lift-off method have been made, as described in U.S. Pat. Nos. 3,849,136 and 3,873,361, all of which patents are assigned to the present assignee. The basic lift-off method for forming a metallurgy pattern does not overcome the non-planarity problem discussed heretofore.
A method for forming a planar metallurgy pattern utilizing the lift-off method is described in U.S. Pat. No. 3,985,597, assigned to the present assignee. The method of this patent involves depositing a conductive metal layer in the bottom of a trench formed in a first layer of an organic thermal setting polymerized resin material, a second overlying layer of a material that is soluble in a solvent that does not appreciably affect the material of the first layer and a third layer resistant to reactive ion etching in O.sub.2. As usual with lift-off methods, the substrate is exposed to a solvent that is selective to the material of the second layer so as to lift-off the structure above the deposited metal and the first layer. Also, as common to the lift-off method, over etching of the masking layer produces an overhang of the openings in the overlying layers. The over etching is used to facilitate easy lift-off of the unwanted portions of the finally deposited layers. The use of an overhang and vertical metal deposition results in small spaces existing between the metal pattern and the surrounding organic resin material of the first layer. The use of an over hang in effect restricts the size of the metal pattern that can be deposited since the spaces formed between the metal pattern and the surrounding organic resin cannot be utilized for metal.